Hybrid vehicles and electric vehicles have high-voltage batteries and power conversion apparatus. The high-voltage battery supplies electric power to the power conversion apparatus that drives a motor for driving a vehicle. The power conversion apparatus is provided with a DC-to-DC converter that converts a high voltage supplied from the high-voltage battery to a low voltage. The low voltage converted by the DC-to-DC converter is supplied to auxiliary devices of the vehicle, such as lamps and a radio.
JP 2013-211943 A, which corresponds to US 2015/0029666 A1, discloses a power conversion apparatus including a power semiconductor module and a DC-to-DC converter. The power semiconductor module converts a DC voltage into an AC voltage. The DC-to-DC converter converts a DC voltage to a DC voltage with a different level.